Conventionally, an organic resin-coated metal sheet which is formed by directly applying an organic resin in a molten state by heating to a metal sheet is manufactured using a manufacturing method and a manufacturing apparatus shown in FIG. 2, for example.
That is, the manufacturing method includes following steps.
1) An elongated strip-shaped metal sheet 1 is continuously fed (downwardly in the drawing) from a metal-sheet supply means not shown in the drawing.
2) An organic resin 2 in a molten state by heating using a heating/melting means not shown in the drawing is discharged from a die lip of a T-die 3, and the organic resin 2 in a molten state by heating extruded in a film shape is allowed to drop on surfaces of pre-rolls 4 arranged between the T-die 3 and lamination rolls 5 for decreasing a neck-in phenomenon of the organic resin 2 thus making a thickness of the film uniform. In the drawing, an arrow indicates the traveling direction of the metal sheet.
3) The organic resin 2 in a molten state by heating which is allowed to drop on the surfaces of the pre-rolls 4 and is brought into contact with the surfaces of the pre-rolls 4 is introduced to the continuously-fed metal sheet 1. Using a pair of lamination rolls 5 arranged immediately downstream of the pre-rolls 4, the metal sheet 1 and the organic resin 2 are nipped and compression-bonded to each other so that an organic resin film is laminated to both surfaces of the metal sheet 1 thus manufacturing an organic-resin coated metal sheet 10.
In manufacturing the organic-resin coated metal sheet using such a conventional manufacturing method, when the organic resin 2 in a molten state by heating is continuously discharged from the T-die 3 and is dropped on and brought into contact with the surfaces of the pre-rolls 4, an oligomer in the molten resin is continuously laminated to the surfaces of the pre-rolls 4. When a predetermined quantity or more of the oligomer is laminated to the surfaces of the pre-rolls 4, the oligomer partially falls as a block and adheres to the molten resin and hence, the oligomer in a block shape adheres to the metal sheet 1 thus causing a serious deterioration in quality. In a step of directly manufacturing a resin film or a resin sheet by continuously discharging an organic resin in a molten state by heating from a T-die, it is possible to ensure a space sufficient for installing a removing device such as a brush or a suction device for cleaning rolls in the vicinity of forming rolls or cooling rolls and hence, an oligomer which adheres to these rolls can be continuously removed without stopping the manufacturing step. However, in a so-called manufacturing step of an extruded lamination material which continuously discharges an organic resin from a T-die and laminates the organic resin to a metal sheet, it is difficult to ensure a space for installing such a removing device. Accordingly, it is necessary to remove an oligomer adhered to rolls by frequently stopping the manufacturing step thus lowering the productivity of an organic-resin coated metal sheet.
As a method of removing an adhered material on a surface of a roll used in the manufacture of a thermoplastic resin film, patent document 1 proposes a method which removes the adhered material by radiating ultraviolet rays to the surface of the roll. Although this method can sufficiently remove an oligomer laminated to a stretching roller used for stretching the thermoplastic resin film in the longitudinal direction and precipitating in a state that the resin is solidified, the method cannot sufficiently remove an oligomer precipitating on a pre-roll with which a resin in a molten state by heating come into contact.
As patent document which discloses the related art, the following document is known.    Patent document 1: JP-A-2001-341196